Saturation carrying capacity of gas and flow regimes in CFB.

Abstract

This paper presents a generalized approach to the saturation carrying capacity of gas, Gs*, in high-velocity fluidized beds. Starting from discussion of the variation of solid holdup in the dense region of circulating fluidized beds (CFBs) with the solid circulation rate, we defined the saturation carrying capacity of gas, Gs*, as the solid circulation rate at which a maximum achievable or saturation solids concentration at the dense region of the CFB starts to be reached. It has been experimentally demonstrated that above Gs*, solid concentrations in the dense region are really independent of changes in the solid circulation rate, the riser diameter, solids feeding system and the solids inventory, and a characteristic S-shaped axial solid holdup distribution would be observed. Based on this physical phenomenon, the saturation carrying capacity of gas was determined as functions of gas velocity and gas-solid properties, and a generalized correlation was therefore proposed on the basis of collected literature data. Finally, a flow diagram in which the flow conditions for occurring of S-shaped and exponential profiles of solids holdup was presented.